Wireless Local Area Networks (LANs) are a popular and inexpensive way to allow multiple users of “mobile units” (MUs) to communicate with each other, to access a wired LAN, to access a local server, to access a remote server, such as over the Internet, etc. Wireless LANs are employed within facilities such as businesses, university classrooms or buildings, airport lounges, hotel meeting rooms, etc. When a user is physically located in the vicinity of an access point, the transceiver of the mobile unit communicates with the access point and a connection to the wireless LAN is established.
A LAN may also include one or more Virtual Local Area Networks (VLANs). A VLAN includes a group of devices with a common set of requirements that communicate as if they were attached to the same broadcast domain, regardless of their physical location. A VLAN has the same attributes as a physical LAN, but allows for devices to be grouped together even if they are not located on the same network switch. Conventional VLANs were statically configured on wired networks using the Institute of Electrical and Electronics Engineers (IEEE) 802.1Q networking standard. Typically, Virtual Local Area Networks (VLANs) are governed by a set of policies relating to network security, user permissions and the like.
Wireless LANs may allow a mobile unit to send/receive an Internet Protocol (IP) multicast stream. IP multicast is a technique for one-to-many communication over an IP infrastructure in a network. IP multicast is widely deployed in enterprises, commercial stock exchanges, and multimedia content delivery networks. A common enterprise use of IP multicast is for IPTV applications such as distance learning and televised company meetings. It scales to a larger receiver population by not requiring prior knowledge of who or how many receivers there are. Multicast uses network infrastructure efficiently by requiring the source to send a packet only once, even if it needs to be delivered to a large number of receivers. Internet Protocol networks use the Internet Group Management Protocol (IGMP) to support efficient multicast. Multicast streams are destined to multicast group IP addresses and are replicated by multicast router nodes only on those downstream ports where a receiver(s) has requested to join the multicast stream.
IGMP snooping is a mechanism used by Layer 2 switching nodes in the network to optimize the flow of multicast traffic within a broadcast domain. IGMP snooping operates on a switch by snooping the IGMP protocol's multicast group join and leave requests from multicast receivers downstream per Virtual Local Area Network (VLAN). IGMP join and leave requests are sent by the receivers based on periodic queries from the upstream IGMP multicast routers or IGMP proxy queriers based on protocol timers. IGMP snooping switches do not initiate these queries by themselves. Multicast traffic for a specific multicast group is forwarded to only those downstream ports where a snooping switch has detected the receiver for the multicast group from the snooped IGMP messages.